PROJECT SUMMARY/ABSTRACT Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor in the gastrointestinal tract, mostly originated from the stomach and small intestine, but anywhere from the esophagus to the rectum. The standard of care for GIST patients with a primary tumor is surgery, aiming for a macroscopically complete resection with negative microscopic margins. Complete resection is possible in the majority of localized GISTs, but only approximately one-half remain recurrence-free for five or more years with surgery alone. Additionally, about 30% of malignant GISTs exhibit metastasis and infiltration, which are difficult to find using conventional endoscopic assessments and CT scanning. GIST is frequently characterized by the overexpression of tyrosine-protein kinase (KIT) and platelet-derived growth factor receptor alpha (PDGFRA) gene mutations. Imatinib mesylate (STI571; Gleevec, Novartis) is a selective tyrosine kinase inhibitor that targets of KIT/PDGFRA and inhibits multiple signaling pathways. Imatinib was originally used for metastatic or unresectable GISTs with patients showing clinical responses in up to 80% of cases, and the current FDA-approved treatments include the use of imatinib in the adjuvant setting following complete gross resection of KIT-positive tumors to prevent recurrence. The complete resection of tumors with an intact pseudocapsule and negative microscopic margin improves the prognosis of the patients. However, most GIST surgeries are still performed ?blindly? without any efficient of intraoperative image guidance for tumor margin and without an ideal verification of other occult metastases in the surgical field. Our hypothesis is that near-infrared nanoprobes targeted to GISTs will provide surgeons with sensitive, specific, and real-time intraoperative image-guidance after a single preoperative injection. Recently, we have developed renal clearable organic nanoparticles (H-Dots) for diagnosis, staging, and treatment of cancers (Kang et al. Adv. Mater. 2016). By combining imatinib in the cavity of H-dot nanoprobes, we could achieve GIST-specific delivery via systemic circulation and rapid distribution as well as renal excretion after complete targeting to the tumor site without nonspecific uptake. We could also resect GISTs with real-time intraoperative guidance for accurate tumor margin in the surgical field. In this proposal, we propose to use these targeted nanoprobes for active treatment of GIST in xenograft and genetically engineered GIST animal models. The real-time intraoperative imaging system will allow us to see the GIST ?glowing? on the screen, thus permitting image-guided resection of small tumors with clear surgical margins. Furthermore, GIST-specific anticancer drug imatinib will inhibit KIT expression at the cellular level in small and undetectable metastatic tumors. The goal of this study is clinical translation of theranostic H-dots for image-guided surgery and treatment of GIST. This novel approach has the potential to revolutionize the development of therapeutic interventions of cancer and nanomedicine.